A novel form of cellular communication among thymic epithelial cells: intercellular calcium wave propagation

The single-cell transcriptome of mTECs and CD4+ thymocytes under adhesion revealed heterogeneity of mTECs and a network controlled by Aire and lncRNAs

To further understand the impact of deficiency of the autoimmune regulator (Aire) gene during the adhesion of medullary thymic epithelial cells (mTECs) to thymocytes, we sequenced single-cell libraries (scRNA-seq) obtained from Aire wild-type (WT) (Airewt/wt ) or Aire-deficient (Airewt/mut ) mTECs cocultured with WT single-positive (SP) CD4+ thymocytes. Although the libraries differed in their mRNA and long noncoding RNA (lncRNA) profiles, indicating that mTECs were heterogeneous in terms of their transcriptome, UMAP clustering revealed that both mTEC lines expressed their specific markers, i.e., Epcam, Itgb4, Itga6, and Casp3 in resting mTECs and Ccna2, Pbk, and Birc5 in proliferative mTECs. Both cocultured SP CD4+ thymocytes remained in a homogeneous cluster expressing the Il7r and Ccr7 markers. Comparisons of the two types of cocultures revealed the differential expression of mRNAs that encode transcription factors (Zfpm2, Satb1, and Lef1), cell adhesion genes (Itgb1) in mTECs, and Themis in thymocytes, which is associated with the regulation of positive and negative selection. At the single-cell sequencing resolution, we observed that Aire acts on both Aire WT and Aire-deficient mTECs as an upstream controller of mRNAs, which encode transcription factors or adhesion proteins that, in turn, are posttranscriptionally controlled by lncRNAs, for example, Neat1, Malat1, Pvt1, and Dancr among others. Under Aire deficiency, mTECs dysregulate the expression of MHC-II, CD80, and CD326 (EPCAM) protein markers as well as metabolism and cell cycle-related mRNAs, which delay the cell cycle progression. Moreover, when adhered to mTECs, WT SP CD4+ or CD8+ thymocytes modulate the expression of cell activation proteins, including CD28 and CD152/CTLA4, and the expression of cellular metabolism mRNAs. These findings indicate a complex mechanism through which an imbalance in Aire expression can affect mTECs and thymocytes during adhesion.

Endoplasmic Reticulum Calcium Mediates Drosophila Wing Development

Background

The temporal dynamics of morphogen presentation impacts transcriptional responses and tissue patterning. However, the mechanisms controlling morphogen release are far from clear. We found that inwardly rectifying potassium (Irk) channels regulate endogenous transient increases in intracellular calcium and bone morphogenetic protein (BMP/Dpp) release for Drosophila wing development. Inhibition of Irk channels reduces BMP/Dpp signaling, and ultimately disrupts wing morphology. Ion channels impact development of several tissues and organisms in which BMP signaling is essential. In neurons and pancreatic beta cells, Irk channels modulate membrane potential to affect intracellular Ca++ to control secretion of neurotransmitters and insulin. Based on Irk activity in neurons, we hypothesized that electrical activity controls endoplasmic reticulum (ER) Ca++ release into the cytoplasm to regulate the release of BMP.

Materials and Methods

To test this hypothesis, we reduced expression of four proteins that control ER calcium, Stromal interaction molecule 1 (Stim), Calcium release-activated calcium channel protein 1 (Orai), SarcoEndoplasmic Reticulum Calcium ATPase (SERCA), small conductance calcium-activated potassium channel (SK), and Bestrophin 2 (Best2) using RNAi and documented wing phenotypes. We use live imaging to study calcium and Dpp release within pupal wings and larval wing discs. Additionally, we employed immunohistochemistry to characterize Small Mothers Against Decapentaplegic (SMAD) phosphorylation downstream of the BMP/Dpp pathway following RNAi knockdown.

Results

We found that reduced Stim and SERCA function decreases amplitude and frequency of endogenous calcium transients in the wing disc and reduced BMP/Dpp release.

Conclusion

Our results suggest control of ER calcium homeostasis is required for BMP/Dpp release, and Drosophila wing development.

miR-155 exerts posttranscriptional control of autoimmune regulator (Aire) and tissue-restricted antigen genes in medullary thymic epithelial cells

BACKGROUND

The autoimmune regulator (Aire) gene is critical for the appropriate establishment of central immune tolerance. As one of the main controllers of promiscuous gene expression in the thymus, Aire promotes the expression of thousands of downstream tissue-restricted antigen (TRA) genes, cell adhesion genes and transcription factor genes in medullary thymic epithelial cells (mTECs). Despite the increasing knowledge about the role of Aire as an upstream transcriptional controller, little is known about the mechanisms by which this gene could be regulated.

RESULTS

Here, we assessed the posttranscriptional control of Aire by miRNAs. The in silico miRNA-mRNA interaction analysis predicted thermodynamically stable hybridization between the 3'UTR of Aire mRNA and miR-155, which was confirmed to occur within the cellular milieu through a luciferase reporter assay. This finding enabled us to hypothesize that miR-155 might play a role as an intracellular posttranscriptional regulator of Aire mRNA. To test this hypothesis, we transfected a murine mTEC cell line with a miR-155 mimic in vitro, which reduced the mRNA and protein levels of Aire. Moreover, large-scale transcriptome analysis showed the modulation of 311 downstream mRNAs, which included 58 TRA mRNAs. Moreover, miR-155 mimic-transfected cells exhibited a decrease in their chemotaxis property compared with control thymocytes.

CONCLUSION

Overall, the results indicate that miR-155 may posttranscriptionally control Aire mRNA, reducing the respective Aire protein levels; consequently, the levels of mRNAs encode tissue-restricted antigens were affected. In addition, miR-155 regulated a crucial process by which mTECs allow thymocytes' migration through chemotaxis.

The absence of the autoimmune regulator gene (AIRE) impairs the three-dimensional structure of medullary thymic epithelial cell spheroids

Background

Besides controlling the expression of peripheral tissue antigens, the autoimmune regulator (AIRE) gene also regulates the expression of adhesion genes in medullary thymic epithelial cells (mTECs), an essential process for mTEC-thymocyte interaction for triggering the negative selection in the thymus. For these processes to occur, it is necessary that the medulla compartment forms an adequate three-dimensional (3D) architecture, preserving the thymic medulla. Previous studies have shown that AIRE knockout (KO) mice have a small and disorganized thymic medulla; however, whether AIRE influences the mTEC-mTEC interaction in the maintenance of the 3D structure has been little explored. Considering that AIRE controls cell adhesion genes, we hypothesized that this gene affects 3D mTEC-mTEC interaction. To test this, we constructed an in vitro model system for mTEC spheroid formation, in which cells adhere to each other, establishing a 3D structure.

Results

The comparisons between AIRE wild type (AIRE^WT) and AIRE KO (AIRE^−/−) 3D mTEC spheroid formation showed that the absence of AIRE: i) disorganizes the 3D structure of mTEC spheroids, ii) increases the proportion of cells at the G0/G1 phase of the cell cycle, iii) increases the rate of mTEC apoptosis, iv) decreases the strength of mTEC-mTEC adhesion, v) promotes a differential regulation of mTEC classical surface markers, and vi) modulates genes encoding adhesion and other molecules.

Conclusions

Overall, the results show that AIRE influences the 3D structuring of mTECs when these cells begin the spheroid formation through controlling cell adhesion genes.

Mechanisms Underlying Influence of Bioelectricity in Development

To execute the intricate process of development, cells coordinate across tissues and organs to determine where each cell divides and differentiates. This coordination requires complex communication between cells. Growing evidence suggests that bioelectrical signals controlled via ion channels contribute to cell communication during development. Ion channels collectively regulate the transmembrane potential of cells, and their function plays a conserved role in the development of organisms from flies to humans. Spontaneous calcium oscillations can be found in nearly every cell type and tissue, and disruption of these oscillations leads to defects in development. However, the mechanism by which bioelectricity regulates development is still unclear. Ion channels play essential roles in the processes of cell death, proliferation, migration, and in each of the major canonical developmental signaling pathways. Previous reviews focus on evidence for one potential mechanism by which bioelectricity affects morphogenesis, but there is evidence that supports multiple different mechanisms which are not mutually exclusive. Evidence supports bioelectricity contributing to development through multiple different mechanisms. Here, we review evidence for the importance of bioelectricity in morphogenesis and provide a comprehensive review of the evidence for several potential mechanisms by which ion channels may act in developmental processes.

Autoimmune regulator act in synergism with thymocyte adhesion in the control of lncRNAs in medullary thymic epithelial cells

The autoimmune regulator (Aire) gene in medullary thymic epithelial cells (mTECs) encodes the AIRE protein, which interacts with its partners within the nucleus. This "Aire complex" induces stalled RNA Pol II on chromatin to proceed with transcription elongation of a large set of messenger RNAs and microRNAs. Considering that RNA Pol II also transcribes long noncoding RNAs (lncRNAs), we hypothesized that Aire might be implicated in the upstream control of this RNA species. To test this, we employed a loss-of-function approach in which Aire knockout mTECs were compared to Aire wild-type mTECs for lncRNA transcriptional profiling both in vitro and in vivo model systems. RNA sequencing enables the differential expression profiling of lncRNAs when these cells adhere in vitro to thymocytes or do not adhere to them as a way to test the effect of cell adhesion. Sets of lncRNAs that are unique and that are shared in vitro and in vivo were identified. Among these, we found the Aire-dependent lncRNAs as for example, Platr28, Ifi30, Morrbid, Malat1, and Xist. This finding represents the first evidence that Aire mediates the transcription of lncRNAs in mTECs. Microarray hybridizations enabled us to observe that temporal thymocyte adhesion modulates the expression levels of such lncRNAs as Morrbid, Xist, and Fbxl12o after 36 h of adhesion. This finding shows the existence of a synergistic mechanism involving a link between thymocyte adhesion, Aire, and lncRNAs in mTECs that might be important for immune self-representation.

Adhesion between medullary thymic epithelial cells and thymocytes is regulated by miR-181b-5p and miR-30b

In this work, we demonstrate that adhesion between medullary thymic epithelial cells (mTECs) and thymocytes is controlled by miRNAs. Adhesion between mTECs and developing thymocytes is essential for triggering negative selection (NS) of autoreactive thymocytes that occurs in the thymus. Immune recognition is mediated by the MHC / TCR receptor, whereas adhesion molecules hold cell-cell interaction stability. Indeed, these processes must be finely controlled, if it is not, it may lead to aggressive autoimmunity. Conversely, the precise molecular genetic control of mTEC-thymocyte adhesion is largely unclear. Here, we asked whether miRNAs would be controlling this process through the posttranscriptional regulation of mRNAs that encode adhesion molecules. For this, we used small interfering RNA to knockdown (KD) Dicer mRNA in vitro in a murine mTEC line. A functional assay with fresh murine thymocytes co-cultured with mTECs showed that single-positive (SP) CD4 and CD8 thymocyte adhesion was increased after Dicer KD and most adherent subtype was CD8 SP cells. Analysis of broad mTEC transcriptional expression showed that Dicer KD led to the modulation of 114 miRNAs and 422 mRNAs, including those encoding cell adhesion or extracellular matrix proteins, such as Lgals9, Lgals3pb, Tnc and Cd47. Analysis of miRNA-mRNA networks followed by miRNA mimic transfection showed that these mRNAs are under the control of miR-181b-5p and miR-30b*, which may ultimately control mTEC-thymocyte adhesion. The expression of CD80 surface marker in mTECs was increased after Dicer KD following thymocyte adhesion. This indicates the existence of new mechanisms in mTECs that involve the synergistic action of thymocyte adhesion and regulatory miRNAs.

Intercellular Ca2+ signalling in the adult mouse cochlea

KEY POINTS

Intercellular Ca²⁺ waves are increases in cytoplasmic Ca²⁺ levels that propagate between cells. Periodic Ca²⁺ waves have been linked to gene regulation and are thought to play a crucial role in the development of our hearing epithelium, the organ of Corti and the acquisition of hearing. We observed regular periodic intercellular Ca²⁺ waves in supporting cells of an ex vivo preparation of the adult mouse organ of Corti, and these waves were found to propagate independently of extracellular ATP and were inhibited by the gap junction blockers 1-octanol and carbenoxolone. Our results establish that the existence of periodic Ca²⁺ waves in the organ of Corti is not restricted to the prehearing period.

ABSTRACT

We have investigated wave-like cytoplasmic calcium (Ca²⁺ ) signalling in an ex vivo preparation of the adult mouse organ of Corti. Two types of intercellular Ca²⁺ waves that differ in propagation distance and speed were observed. One type was observed to travel up to 100 μm with an average velocity of 7 μm/s. Such waves were initiated by local tissue damage in the outer hair cell region. The propagation distance was decreased when the purinergic receptor antagonists pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS; 50 μm) or suramin (150 μm) were added to the extracellular buffer. Immunocytochemical analysis and experiments with calcium indicator dyes showed that both P2X and P2Y receptors were present in supporting cells. A second class of waves identified to travel longitudinally along the organ of Corti propagated at a lower velocity of 1-3 μm/s. These 'slow' Ca²⁺ waves were particularly evident in the inner sulcus and Deiters' cells. They travelled for distances of up to 500 μm. The slow Ca²⁺ signalling varied periodically (approximately one wave every 10 min) and was maintained for more than 3 h. The slow waves were not affected by apyrase, or by the P2 receptor agonists suramin (150 μm) or PPADS (50 μm) but were blocked by the connexin channel blockers octanol (1 mm) and carbenoxolone (100 μm). It is proposed that the observed Ca²⁺ waves might be a physiological response to a change in extracellular environment and may be involved in critical gene regulation activities in the supporting cells of the cochlea.

Aire Disruption Influences the Medullary Thymic Epithelial Cell Transcriptome and Interaction With Thymocytes

The function of medullary thymic epithelial cells (mTECs) is associated with thymocyte adhesion, which is crucial for the negative selection of autoreactive thymocytes in the thymus. This process represents the root of central tolerance of self-components and prevents the onset of autoimmune diseases. Since thymic epithelia correspond to an important target of donor T cells during the onset of chronic graft-vs-host-disease, mTEC-thymocyte adhesion may have implications for alloimmunity. The Aire and Fezf2 genes function as transcriptome controllers in mTECs. The central question of this study is whether there is a mutual relationship between mTEC-thymocyte adhesion and the control of the mTEC transcriptome and whether Aire is involved in this process. Here, we show that in vitro mTEC-thymocyte adhesion causes transcriptome changes in mTECs and upregulates the transcriptional expression of Aire and Fezf2, as well as cell adhesion-related genes such as Cd80 or Tcf7, among others. Crispr-Cas9-mediated Aire gene disruption demonstrated that this gene plays a role in the process of mTEC-thymocyte adhesion. Consistent with the nuclear localization signal (NLS) encoded by Aire exon 3, which was targeted, we demonstrate that Aire KO-/- mTECs impair AIRE protein localization in the nucleus. Consequently, the loss of function of Aire reduced the ability of these cells to adhere to thymocytes. Their transcriptomes differed from their wild-type Aire+/+ counterparts, even during thymocyte adhesion. A set of mRNA isoforms that encode proteins involved in cell adhesion were also modulated during this process. This demonstrates that both thymocyte interactions and Aire influence transcriptome profiling of mTEC cells.

Single-cell Microinjection for Cell Communication Analysis

Gap junctions are intercellular channels that allow the communication of neighboring cells. This communication depends on the contribution of a hemichannel by each neighboring cell to form the gap junction. In mammalian cells, the hemichannel is formed by six connexins, monomers with four transmembrane domains and a C and N terminal within the cytoplasm. Gap junctions permit the exchange of ions, second messengers, and small metabolites. In addition, they have important roles in many forms of cellular communication within physiological processes such as synaptic transmission, heart contraction, cell growth and differentiation. We detail how to perform a single-cell microinjection of Lucifer Yellow to visualize cellular communication via gap-junctions in living cells. It is expected that in functional gap junctions, the dye will diffuse from the loaded cell to the connected cells. It is a very useful technique to study gap junctions since you can evaluate the diffusion of the fluorescence in real time. We discuss how to prepare the cells and the micropipette, how to use a micromanipulator and inject a low molecular weight fluorescent dye in an epithelial cell line.

Calcium spikes, waves and oscillations in a large, patterned epithelial tissue

While calcium signaling in excitable cells, such as muscle or neurons, is extensively characterized, calcium signaling in epithelial tissues is little understood. Specifically, the range of intercellular calcium signaling patterns elicited by tightly coupled epithelial cells and their function in the regulation of epithelial characteristics are little explored. We found that in Drosophila imaginal discs, a widely studied epithelial model organ, complex spatiotemporal calcium dynamics occur. We describe patterns that include intercellular waves traversing large tissue domains in striking oscillatory patterns as well as spikes confined to local domains of neighboring cells. The spatiotemporal characteristics of intercellular waves and oscillations arise as emergent properties of calcium mobilization within a sheet of gap-junction coupled cells and are influenced by cell size and environmental history. While the in vivo function of spikes, waves and oscillations requires further characterization, our genetic experiments suggest that core calcium signaling components guide actomyosin organization. Our study thus suggests a possible role for calcium signaling in epithelia but importantly, introduces a model epithelium enabling the dissection of cellular mechanisms supporting the initiation, transmission and regeneration of long-range intercellular calcium waves and the emergence of oscillations in a highly coupled multicellular sheet.

Aire knockdown in medullary thymic epithelial cells affects Aire protein, deregulates cell adhesion genes and decreases thymocyte interaction

We demonstrate that even a partial reduction of Aire mRNA levels by siRNA-induced Aire knockdown (Aire KD) has important consequences to medullary thymic epithelial cells (mTECs). Aire knockdown is sufficient to reduce Aire protein levels, impair its nuclear location, and cause an imbalance in large-scale gene expression, including genes that encode cell adhesion molecules. These genes drew our attention because adhesion molecules are implicated in the process of mTEC-thymocyte adhesion, which is critical for T cell development and the establishment of central self-tolerance. Accordingly, we consider the following: 1) mTECs contribute to the elimination of self-reactive thymocytes through adhesion; 2) Adhesion molecules play a crucial role during physical contact between these cells; and 3) Aire is an important transcriptional regulator in mTECs. However, its role in controlling mTEC-thymocyte adhesion remains unclear. Because Aire controls adhesion molecule genes, we hypothesized that the disruption of its expression could influence mTEC-thymocyte interaction. To test this hypothesis, we used a murine Aire(+) mTEC cell line as a model system to reproduce mTEC-thymocyte adhesion in vitro. Transcriptome analysis of the mTEC cell line revealed that Aire KD led to the down-modulation of more than 800 genes, including those encoding for proteins involved in cell adhesion, i.e., the extracellular matrix constituent Lama1, the CAM family adhesion molecules Vcam1 and Icam4, and those that encode peripheral tissue antigens. Thymocytes co-cultured with Aire KD mTECs had a significantly reduced capacity to adhere to these cells. This finding is the first direct evidence that Aire also plays a role in controlling mTEC-thymocyte adhesion.

Connexin43 knockdown in bone marrow‑derived dendritic cells by small interfering RNA leads to a diminished T-cell stimulation

Dendritic cells, the most powerful type of antigen‑presenting cells, have the unique ability to induce primary immune responses. Connexin43 expression is upregulated to increase gap junctions when immune cells are exposed to inflammatory factors. The present study applied small‑interfering RNA (siRNA) to decrease connexin43 expression. The results showed that silencing of connexin43 using siRNA resulted in arrest of bone marrow‑derived dendritic cell (BM‑DC) maturation as evidenced by reduced expression of major histocompatibility complex II, CD40, CD80 and CD86. Functionally, connexin43‑silenced BM‑DC showed a markedly decreased capability to induce T-cell stimulation. In conclusion, the present study demonstrated that antigens present on BM‑DCs can be suppressed by connexin43 knockdown in BM‑DCs. The present study therefore presented an effective method to modulate the immunology of BM‑DCs.

Focal activation of cells by plasmon resonance assisted optical injection of signaling molecules

Experimental methods for single cell intracellular delivery are essential for probing cell signaling dynamics within complex cellular networks, such as those making up the tumor microenvironment. Here, we show a quantitative and general method of interrogation of signaling pathways. We applied highly focused near-infrared laser light to optically inject gold-coated liposomes encapsulating bioactive molecules into single cells for focal activation of cell signaling. For this demonstration, we encapsulated either inositol trisphosphate (IP3), an endogenous cell signaling second messenger, or adenophostin A (AdA), a potent analogue of IP, within 100 nm gold-coated liposomes, and injected these gold-coated liposomes and their contents into the cytosol of single ovarian carcinoma cells to initiate calcium (Ca(2+)) release from intracellular stores. Upon optical injection of IP3 or AdA at doses above the activation threshold, we observed increases in cytosolic Ca(2+) concentration within the injected cell initiating the propagation of a Ca(2+) wave throughout nearby cells. As confirmed by octanol-induced inhibition, the intercellular Ca(2+) wave traveled via gap junctions. Optical injection of gold-coated liposomes represents a quantitative method of focal activation of signaling cascades of broad interest in biomedical research.

Purinergic signalling in endocrine organs

There is widespread involvement of purinergic signalling in endocrine biology. Pituitary cells express P1, P2X and P2Y receptor subtypes to mediate hormone release. Adenosine 5'-triphosphate (ATP) regulates insulin release in the pancreas and is involved in the secretion of thyroid hormones. ATP plays a major role in the synthesis, storage and release of catecholamines from the adrenal gland. In the ovary purinoceptors mediate gonadotrophin-induced progesterone secretion, while in the testes, both Sertoli and Leydig cells express purinoceptors that mediate secretion of oestradiol and testosterone, respectively. ATP released as a cotransmitter with noradrenaline is involved in activities of the pineal gland and in the neuroendocrine control of the thymus. In the hypothalamus, ATP and adenosine stimulate or modulate the release of luteinising hormone-releasing hormone, as well as arginine-vasopressin and oxytocin. Functionally active P2X and P2Y receptors have been identified on human placental syncytiotrophoblast cells and on neuroendocrine cells in the lung, skin, prostate and intestine. Adipocytes have been recognised recently to have endocrine function involving purinoceptors.

The importance of the nurse cells and regulatory cells in the control of T lymphocyte responses

T lymphocytes from the immune system are bone marrow-derived cells whose development and activities are carefully supervised by two sets of accessory cells. In the thymus, the immature young T lymphocytes are engulfed by epithelial “nurse cells” and retained in vacuoles, where most of them (95%) are negatively selected and removed when they have an incomplete development or express high affinity autoreactive receptors. The mature T lymphocytes that survive to this selection process leave the thymus and are controlled in the periphery by another subpopulation of accessory cells called “regulatory cells,” which reduce any excessive immune response and the risk of collateral injuries to healthy tissues. By different times and procedures, nurse cells and regulatory cells control both the development and the functions of T lymphocyte subpopulations. Disorders in the T lymphocytes development and migration have been observed in some parasitic diseases, which disrupt the thymic microenvironment of nurse cells. In other cases, parasites stimulate rather than depress the functions of regulatory T cells decreasing T-mediated host damages. This paper is a short review regarding some features of these accessory cells and their main interactions with T immature and mature lymphocytes. The modulatory role that neurotransmitters and hormones play in these interactions is also revised.

Intercellular Ca(2+) waves: mechanisms and function

Intercellular calcium (Ca(2+)) waves (ICWs) represent the propagation of increases in intracellular Ca(2+) through a syncytium of cells and appear to be a fundamental mechanism for coordinating multicellular responses. ICWs occur in a wide diversity of cells and have been extensively studied in vitro. More recent studies focus on ICWs in vivo. ICWs are triggered by a variety of stimuli and involve the release of Ca(2+) from internal stores. The propagation of ICWs predominately involves cell communication with internal messengers moving via gap junctions or extracellular messengers mediating paracrine signaling. ICWs appear to be important in both normal physiology as well as pathophysiological processes in a variety of organs and tissues including brain, liver, retina, cochlea, and vascular tissue. We review here the mechanisms of initiation and propagation of ICWs, the key intra- and extracellular messengers (inositol 1,4,5-trisphosphate and ATP) mediating ICWs, and the proposed physiological functions of ICWs.

Thymus atrophy and double-positive escape are common features in infectious diseases

The thymus is a primary lymphoid organ in which bone marrow-derived T-cell precursors undergo differentiation, leading to migration of positively selected thymocytes to the T-cell-dependent areas of secondary lymphoid organs. This organ can undergo atrophy, caused by several endogenous and exogenous factors such as ageing, hormone fluctuations, and infectious agents. This paper will focus on emerging data on the thymic atrophy caused by infectious agents. We present data on the dynamics of thymus lymphocytes during acute Trypanosoma cruzi infection, showing that the resulting thymus atrophy comprises the abnormal release of thymic-derived T cells and may have an impact on host immune response.

Age-related deregulation of Aire and peripheral tissue antigen genes in the thymic stroma of non-obese diabetic (NOD) mice is associated with autoimmune type 1 diabetes mellitus (DM-1)

Gene expression of peripheral tissue antigens (PTAs) in stromal medullary thymic epithelial cells (mTECs) is a key process to the negative selection of autoreactive thymocytes. This phenomenon was termed "promiscuous gene expression" (PGE), which is partially controlled by the Aire gene. Nevertheless, reasons for the correlation of Aire and PTAs with the emergence of autoimmune diseases are largely unknown, though it may be a result of a chronological effect. Although the effect of Aire mutations in pathogenic autoimmunity is well know, it could not be a unique cause for autoimmunity. Independently of mutations, temporal deregulation of Aire expression may imbalance Aire-dependent PTAs and/or wide PGE. This deregulation may be an early warning sign for autoimmune diseases as it guarantees autoantigen representation in the thymus. To assess this hypothesis, we studied the expression levels of Aire, Aire-dependent (Ins2) and Aire-independent (Gad67 and Col2a1) PTAs using real-time-PCR of the thymic stromal cells of NOD mice during the development of autoimmune type 1 diabetes mellitus (DM-1). Wide PGE was studied by microarrays in which the PTA genes were identified through parallel CD80(+) mTEC 3.10 cell line expression profiling. The results show that Aire gene was down-regulated in young pre-autoimmune (pre-diabetic) NOD mice. PGE and specific PTA genes were down-regulated in adult autoimmune diabetic animals. These findings represent evidence indicating that chronological deregulation of genes important to negative selection may be associated with the development of an autoimmune disease (DM-1) in mice.

Modulatory effects of cAMP and PKC activation on gap junctional intercellular communication among thymic epithelial cells

BACKGROUND

We investigated the effects of the signaling molecules, cyclic AMP (cAMP) and protein-kinase C (PKC), on gap junctional intercellular communication (GJIC) between thymic epithelial cells (TEC).

RESULTS

Treatment with 8-Br-cAMP, a cAMP analog; or forskolin, which stimulates cAMP production, resulted in an increase in dye transfer between adjacent TEC, inducing a three-fold enhancement in the mean fluorescence of coupled cells, ascertained by flow cytometry after calcein transfer. These treatments also increased Cx43 mRNA expression, and stimulated Cx43 protein accumulation in regions of intercellular contacts. VIP, adenosine, and epinephrine which may also signal through cyclic nucleotides were tested. The first two molecules did not mimic the effects of 8-Br-cAMP, however epinephrine was able to increase GJIC suggesting that this molecule functions as an endogenous inter-TEC GJIC modulators. Stimulation of PKC by phorbol-myristate-acetate inhibited inter-TEC GJIC. Importantly, both the enhancing and the decreasing effects, respectively induced by cAMP and PKC, were observed in both mouse and human TEC preparations. Lastly, experiments using mouse thymocyte/TEC heterocellular co-cultures suggested that the presence of thymocytes does not affect the degree of inter-TEC GJIC.

CONCLUSIONS

Overall, our data indicate that cAMP and PKC intracellular pathways are involved in the homeostatic control of the gap junction-mediated communication in the thymic epithelium, exerting respectively a positive and negative role upon cell coupling. This control is phylogenetically conserved in the thymus, since it was seen in both mouse and human TEC preparations. Lastly, our work provides new clues for a better understanding of how the thymic epithelial network can work as a physiological syncytium.

Triiodothyronine modulates thymocyte migration

Triiodothyronine (T(3)) exerts several effects on thymus physiology. In this sense, T(3) is known to stimulate thymic microenvironmental cells to enhance the production of extracellular matrix (ECM) moieties, which are relevant in thymocyte migration. Here, we further investigated the in vivo influence of T(3) on ECM production, as well as on ECM-related T-cell migration events. For this, BALB/c mice were subjected to two protocols of T(3) treatment: long-term (30 days) i.p. daily T(3) injections or short-term (16 h) after a single T(3) intrathymic injection. These two treatments did promote an enhancement in the expression of fibronectin and laminin, in both cortex and medullary regions of the thymic lobules. As revealed by the long-term treatment, the expression of ECM protein receptors, including VLA-4, VLA-5 and VLA-6, was also increased in thymocyte subsets issued from T(3)-treated mice. We further used thymic nurse cells (TNC) as an in vitro system to study the ECM-related migration of immature thymocytes in the context of thymic epithelial cells. Even a single intrathymic injection of T(3) resulted in an increase in the ex vivo exit of thymocytes from TNC lymphoepithelial complexes. Accordingly, when we evaluated thymocyte migration in transwell chambers pre-coated with ECM proteins, we found an increase in the numbers of migrating cells, when thymocytes were derived from T(3)-treated mice. Overall, our data show that in vivo intrathymic short-term i.p. long-term T(3) treatments are able to modulate thymocyte migration, probably via ECM-mediated interactions.

Calcium Dynamics: Spatio‐Temporal Organization from the Subcellular to the Organ Level

Many essential physiological processes are controlled by calcium. To ensure reliability and specificity, calcium signals are highly organized in time and space in the form of oscillations and waves. Interesting findings have been obtained at various scales, ranging from the stochastic opening of a single calcium channel to the intercellular calcium wave spreading through an entire organ. A detailed understanding of calcium dynamics thus requires a link between observations at different scales. It appears that some regulations such as calcium-induced calcium release or PLC activation by calcium, as well as the weak diffusibility of calcium ions play a role at all levels of organization in most cell types. To comprehend how calcium waves spread from one cell to another, specific gap-junctional coupling and paracrine signaling must also be taken into account. On the basis of a pluridisciplinar approach ranging from physics to physiology, a unified description of calcium dynamics is emerging, which could help understanding how such a small ion can mediate so many vital functions in living systems.

Effect of heptanol on noradrenaline-induced contractions in rat vas deferens

We have studied the effects of 1-heptanol and nifedipine on noradrenaline (NA)-induced contractions in order to explore the role of gap junctions and their interactions with L-type Ca2+ channel mediated [Ca2+]o entry in the generation of NA-induced contractions in the rat vas deferens. Application of 20 microM NA to rat vas deferens resulted in contractions with three different components, an initial phasic component followed by a tonic component overlapped with an oscillatory component. Heptanol (0.01-2 mM) induced a concentration dependent reduction of the contractions. 2 mM heptanol reduced the phasic component by 32.9 +/- 4.4% and the tonic component by 93.8 +/- 1.9% of control, while the oscillatory component was completely abolished (n=7). Nifedipine (2 microM) reduced the phasic component by 34.5 +/- 4.1% and the tonic component by 89.5 +/- 3.8% of control and abolished the oscillatory component (n=6). In the presence of heptanol and nifedipine together, the phasic component was reduced by 61.3 +/- 8.3% and the tonic component by 94.5 +/- 1.0% of control. The oscillatory component was completely abolished (n=6). These results allow the conclusion that phasic contraction is mainly due to the direct action of NA, independent of gap junctions, while the tonic and oscillatory contractions may depend significantly on cell-to-cell communication. These in turn may depend critically on the availability of extracellularly derived Ca2+.

Effect of gap junction uncoupler heptanol on resistance arteries reactivity in experimental models of diabetes, hyperlipemia and hyperlipemia-diabetes

The understanding of the involvement of the gap junctions (GJ) in the vascular reactivity is an ongoing effort. In this study we questioned on impact of pathologies such as diabetes, hyperlipemia, and simultaneous hyperlipemia-diabetes on GJ involvement in the contractile/relaxant response of the mesenteric resistance arteries. To this purpose, four groups of Golden Syrian hamsters were used: (i) diabetics (D), injected by streptozotocin, (ii) hyperlipemics (H), fed the standard chow of the species supplemented with 3% cholesterol and 15% butter, (iii) simultaneously hyperlipemic-diabetics (HD), and (iv) controls (C), age-matched normal healthy animals. At 24 weeks after the beginning of the experiment, the vascular reactivity of the resistance arteries was measured by the myograph technique in the presence/absence of 1 mM Heptanol (Hep) and of vasoconstrictors and vasodilators. The results showed that: (i) in pathological conditions 1 mM Hep significantly impaired the constrictor response of the hamster resistance arteries to both 10(-5) M NA (noradrenaline, agonist of alpha(1)-adrenoceptors) and 64.1 mM K+ (potassium ion, the major intracellular cation). The impairment occur in the group range: HD < H < D < C being the highest at the simultaneous insult of hyperlipemia and diabetes; (ii) independently of the pathological condition, 1 mM Hep abolishes both endothelium-dependent and independent relaxation of the hamster resistance arteries. At 1 mM Hep we noticed a reversible effect on endothelium-dependent relaxation that may be partially restored (in normal) in the presence of L-arginine. It is hoped that these results may contribute to understanding of the involvement of GJ in vascular pathology/dysfunction.

Ligament cells stretch-adapted on a microgrooved substrate increase intercellular communication in response to a mechanical stimulus

An in vitro model was used to investigate the effect of mechanical stimuli on adaptation to load and calcium signaling in aligned medial collateral ligament cells (MCL). This model used a patterned silicone membrane to align the cells parallel with the direction of the microgrooves. Alignment created an architecture that simulated a degree of cell orientation in native ligament tissue. It was hypothesized that aligned ligament cells would be more efficient at calcium wave propagation than cells that were randomly oriented. It was further hypothesized that calcium wave propagation would be greater among cells that were both aligned and subjected to mechanical stretch compared to cells that were aligned but not stretched. Rat MCL cells were loaded with Fura-2AM, a calcium-binding dye, and mechanically indented using a micropipette tip. A ratio-imaging fluorescence technique was used to quantitate the calcium (Ca2+) response. It was concluded that stretching ligament cells prior to stimulation increased their sensitivity to load and their ability to propagate a calcium wave. However, the ability of aligned cells to propagate this wave was not significantly different when compared to nonaligned cells. Treatment of cultures with inhibitors such as apyrase and suramin significantly reduced the number of cells recruited in the calcium response. Hence, it was concluded that ATP released from mechanically stimulated cells was a principal mediator responsible for the rise in intracellular calcium in ligament cells. Further, purinoceptor activation may amplify the signal to alert and recruit more cells in a response to mechanical stimulation.